A transmission power of RACH (Random Access Channel) in 3GPP UMTS/LTE is decided based upon a power offset designated by a base station or a fixed power value common to one cell. However, the base station cannot recognize that one mobile station has tried to make a connection to the base station over the RACH until the base station receives the RACH correctly. For this, when the base station is not able to correctly receive the RACH coming from the mobile station, the transmission power cannot be adaptively controlled according to the situation of transmission of the RACH from the mobile station to the base station.
Thereupon, the technology in which the mobile station transmits transmission delay estimation information on the RACH together with a preamble or data and the base station decides a designation value for setting the transmission power of the RACH according to the transmitted transmission delay estimation information is proposed (Patent document 1). Additionally, the transmission delay estimation information is the number of times of transmission or the number of times of retransmission of the data or the preamble, a time elapsed since initial transmission of the data or the preamble, a timing of the initial transmission of the data or the preamble, or the like. Additionally, the so-called preamble is a bit pattern known to the base station, and a signal unknown to the base station such as user data or a control signal is not transmitted as the preamble.
Hereinafter, the case of applying the technology of the Patent document 1 related to the present invention to an E-UTRA system now under consideration in the 3GPP will be explained.
FIG. 22 is a conceptual diagram of the system to which the Patent document 1 related to the present invention is applied. In the system of the technology of the Patent document 1, a plurality of the base station are present adjacently to one another, a plurality of the mobile stations transmit or receive data on a downlink or an uplink to or from each of the base stations, OFDM (Orthogonal Frequency Division Multiple Access) is used for the downlink, and SC-FDMA (Single-Carrier Frequency Division Multiple Access) is used for the uplink. Furthermore, each of the mobile stations and base stations realize functions to be described below by a control program stored in a memory of each of the mobile stations and base stations.
Each base station transmits on the downlink at least a broadcast channel (BCH) for transmitting broadcast information such as system information, a common pilot channel (CPICH) for transmitting a pilot signal, and a common channel (AICH: Acquisition Indicator Channel) for transmitting an acknowledgment signal (ACK signal) in response to uplink data transmission.
FIG. 23 is a sequence diagram illustrating one example of an operation of the above-mentioned system.
One mobile station transmits or receives data based upon the system information transmitted over the BCH, receives the CPICH in a predetermined cycle to ensure synchronization, and measures a reception power of the CPICH (step 1-1). And, the mobile station transmits the preamble over a random access channel (RACH) RACH-1 based upon RACH transmission power information notified over the BCH and a CPICH reception power (Step 1-2).
Herein, when the base station cannot detect the RACH-1, the base station transmits NACK over the AICH without transmitting the ACK (Step 1-3).
Then, the mobile station transmits RACH-2 by increasing the transmission power by a power ramping step size that is included in the RACH transmission power information (Step 1-4).
The base station, upon detecting the RACH-2, transmits the ACK (Step 1-5).
The mobile station, upon receipt of the acknowledgment (after receiving), transmits the transmission delay estimation information over a RACH message part (Step 1-6).
The base station modifies the RACH transmission power information of the BCH based upon the transmission delay estimation information, and transmits it (Step 1-7).
FIG. 24 is a sequence diagram illustrating an example of another operation in the above-mentioned system.
One mobile station transmits or receives data based upon the system information transmitted over the BCH. Further, the mobile station receives the CPICH in a predetermined cycle to ensure synchronization and measures a reception quality of the CPICH (Step 2-1).
When user data or a control signal to be transmitted occurs to the mobile station, the mobile station transmits the transmission delay estimation information using a random access channel (RACH) that is one of uplink wireless channels (Step 2-2). A RACH transmission power at this time is decided based upon a value indicated by the base station using the BCH.
When the base station cannot detect the RACH of the mobile station, the base station does not transmit the ACK over the AICH (Step 2-3). Further, when the base station detects the RACH, the base station transmits the ACK over the AICH (Step 2-5).
When the mobile station transmits the preamble over the RACH, the mobile station receives the random access response over the AICH after a predetermined time, and retransmits the transmission delay estimation information at a predetermined timing until the mobile station receives an acknowledgment signal (ACK signal) indicating that the preamble transmitted by its own station has been correctly received (Step 2-4).
Performing such a process enables the base station to control information on the RACH transmission power indicated by the BCH so that a delay required until the data or the preamble, which is transmitted over the RACH, is correctly received is controlled to an appropriate value, and to reduce interference by setting the transmission power of the mobile station as low as possible while effectively reducing the data transmission delay.                Patent document 1: Publication number: WO2007/052753        